How do I run my external display at full 2560x1440 resolution (with HDMI)?

I believe the maximum resolution that can run over hdmi is 1080p. In order to get your resolution up the the native 2560X1440 you will need to use a dual DVI.

I would guess the system is defaulting to a TV mode, and 1080p is the maximum. Check the TV manual for ways to adjust as the Mac simply adjusts to what is required by the display.

The following might help and it is from this forum:

"The port definitely supports it, but OS X is another story. If I boot into Windows and connect it to a display capable of displaying 2560x1440 over HDMI, it just works. If I'm in OSX, it refuses to allow anything over 1920x1200. Even if I try to force the resolution with SwitchResX, it doesn't work. If I create a custom resolution with a 40Hz refresh rate instead of 60Hz, then it does actually work. 2560x1440 @ 40Hz fits within the bandwidth constraints of a single link at 165MHz. So it appears that OSX limits the port to 1.2 frequencies. I'm not realy sure why -- HDMI 1.4 should allow for frequencies upto 340MHz, and the hardware is clearly capable based on Windows.

Do keep in mind that the cable quality does matter at this resolution. In Windows, one of my cables resulted in extreme artifacts. I switched to another cable I had lying around and it worked perfectly. Weird thing was that the cable that worked was a generic one I got ages ago while the one that artifacted was billed as a high quality item with extra shielding and all that."

By the way, I aam going to buy one of those korean displays. What brand did u buy? R u content with it? Do u have pixle bleed or dead pixel on it? From which did u buy it in ebay? Is DVI--dual link without speaker better or hdmi version with sppeaker?

Thanks in aadvance

While it's not a solution, it's probably one way to exclude another unknown: that your display may have a problem. I got a ASUS PB278 whose specifically list its capability of 2560*1440 over HDMI. Yet, the rMBP failed to achieve that resolution over HDMI, only suggesting a lower resolution (yes, it did work over mDP but I am also not interested in that).

Did you try using switch res to do 2560x1440 @ 40Hz over HDMI? Apperantly that will work -- I'm very intrested to hear if that is a good solution or not.

Did you make sure to use an HDMI 1.4 compatible HDMI cable?

The dual link adapter solution worked for me.